1. Field of the Invention
This invention relates to nuclear fuel rod loaders which load nuclear fuel pellets into fuel rods used in nuclear reactor cores.
2. Description of the Prior Art
The core of a nuclear reactor contains an assembly of fuel rods, arranged so as to generate controlled amounts of heat in specific regions of the reactor core. The fuel rods, approximately twelve feet in length, each contain a column of nuclear fuel pellets extending nearly the full length of the rods. Some of the columns of pellets are organized and arranged in segments, each segment containing different types of fuel pellets varying in quantity of uranium enrichment.
It is critical to the operation of the reactor that these segments of fuel pellets contain the correct type of uranium fuel, that the segments are the correct length and that the segments are situated in the correct longitudinal region of the fuel rods. These factors are critical because the amount of heat generated in specific regions of the reactor core must be controlled to prevent any possibility of overheating. Additionally, nuclear engineers require certain types of fuel in certain longitudinal regions of the fuel rods in order to control the reaction and assist reactor shutdown. Thus, it is important that errors in loading or mixing of the different types of fuel pellets do not occur when the fuel pellets are loaded into the fuel rods.
Experience has shown that previous control methods do not provide the optimum level of accuracy desirable in the nuclear industry for assemblage of nuclear fuel rods. Assembly processes and assembly equipment are desirable which fully insure the degree of quality control required for a reliable system of fuel rod assembly.
In many currently used systems, fuel pellets and fuel rods are assembled and organized on tables, stands and holders with the assembled row of fuel pellets being manually propelled into the fuel rod. These systems have been modified with the use of various types of guide bushings developed to assist the operator in aligning assembled rows of fuel pellets with the center line of the fuel rod so as to facilitate a smooth and damage-free transfer of the pellets into the fuel rod. However, these systems still involve the risk of human failure on the part of the operator and therefore may require multiple checks by other individuals to insure accurate assembly.
U.S. Pat. Nos. 3,940,908 and 3,965,648 disclose improvements over the prior art systems in that preassembled rows of fuel pellets are transferred by mechanical fingers or vibrators into multiple fuel rods. These patents, however, primarily represent an improvement of only one step in the loading operation. The rods themselves must still be placed by hand in the loading position. No provision has been made to automatically weigh the fuel pellets or to measure the length of the fuel pellets as they are loaded into the fuel rods. No automatic safety controls are included in the loading sequence.
It is therefore an object of the present invention to provide an apparatus to assemble a plurality of nuclear fuel pellets in segments, each segment containing a specific type of nuclear fuel, and load the segments into a plurality of fuel rods so that the segments are contained in the correct longitudinal region of the fuel rods, and each segment contains the correct type and amount of fuel.
Another object of the present invention is to provide an apparatus for facilitating assembly of a plurality of nuclear fuel pellets in a row, positioning the row of fuel pellets and the fuel rod in a communicating relationship with each other, transferring the pellets into the fuel rod through a guide bushing and disengaging the guide bushing from the loaded fuel rod.
Another object of the invention is to provide an apparatus which automatically indexes the fuel rods, transfers the proper rod into communicating relationship with the row of fuel pellets at the proper stage in the loading sequence, and moves to index another rod into position after loading of the previous rod has been completed.
Another object of the invention is to provide an apparatus which automatically measures and records the weight and length of the row of pellets currently being loaded and the length of the row of fuel pellets in the final segment which must be loaded into the fuel rod.
Another object of the invention is to provide an apparatus which automatically imposes safety controls on the operation and which interrupts the loading sequence if the assembled length of the row of fuel pellets within the loaded fuel rod, or the weight of the pellets does not fall within certain prescribed limits.